Machine tools, such as CNC mills and CNC machining centers, use a plurality of tools to produce a machined product. Cutting tools, such as end mills and drills, are automatically changed during a machining operation. The cutting tools are typically held in tool holders which are automatically installed and removed from machine spindles, as needed. In order to maintain precise tolerances, the tool holder must be rigidly held within the spindle. If relative movement occurs between the spindle and tool holder, machining errors will result and machining tolerances will be compromised.
A tool holder of the type to which this invention pertains, includes a tapered shank which is received in a complementally-shaped spindle socket. In order to maintain machine tolerances, it is critical that the tapered shank of the tool holder be in intimate and substantially full contact with the spindle socket and that the tool holder be tightly held in the spindle socket.